Grammar/Structure help
 

Hi guys,
I'm using Lang-8 but I need to ask lots of questions as my Japanese is very limited!

I want to say:
'I have a day off on either Wednesday or Thursday'

I know the vocab but I don't know the correct usage/position of 'それとも.'

At a guess I'd say:
水曜日かそれとも木曜日は休暇があります。

But I'm sure that's wrong!

If I well remember それとも is used as conjunction of 2 questions with opposite meaning (eg.will you write the letter by hand or will you type it?).

What you mean with either Wed or Thurs? You don't know which day you have off or you have both days off and you need to pick either one to do something? It could work with 水曜日も木曜日も or 水曜日か木曜日
Sorry, it might be me that don't understand clearly what you mean.

Assuming you mean, say, next week you have one of those days off:
来週、水曜日か木曜日かは休日だ。 (I think this one sounds slightly more casual with か as "or")
来週、水曜日あるいは木曜日は休日だ。 (I think this construction with あるいは as "either ~ or ~" sounds more high-level/professional/whatever)

Of course, other things like だ／です need to be taken into account, too, based on context.